Various techniques are known for digital printers to provide continuous tone (monochrome or color) printing. These techniques include ordered drop dispersion patterns, the building of dot clusters (which look similar to conventional offset halftone printing and are typically printed with very high resolution digital printers such as 1200 dpi), and stochastic (error diffusion) screening.
Digital printing devices are capable of imaging many combinations of primary colors to produce a variety of processed colors. This color set is referred to as the printer gamut. In the case of printers, this set is often ink and media specific. The printer gamut typically consist of thousands of uniquely discernable colors.
Digital printing technology is advancing at a rapid rate. Market acceptance of a number of digital imaging technologies has increased as these technologies become more reliable and convenient to use. Not unlike traditional analog based printing methods, such as photographic techniques, digital imaging quality is highly susceptible to the processing steps performed prior to imaging the digital file.
Color matching is not a new endeavor. Several years ago, the International Color Consortium established standards for mapping one gamut into another. The process involves the generation of a tag file that accompanies the image file. This tag file provides information required to map an entire color gamut from device into that of another. There are several disadvantages of this system. First of all, specific colors are not mapped exactly. Compromises are made to accommodate the entire color set and direct it into the new gamut. Secondly, there is no feedback of the error associated with individual color mapping. Further, there is no way to account for variations in the workflow once the profiles for each device are generated. It is a necessary requirement that the image processing steps remain fixed in order for the profiles to be valid. Finally, there is no predictive capability within the ICC color matching process that will inform a user what transformations are necessary to assure accurate color matching of individual spot colors.
Having the ability to correlate the printed color response to a known input would be very valuable. It would allow one to predict, ahead of time, the color response of the system to a known input. Further, knowing the effects of workflow modifications on printed output would increase the ability to correlate the cause and effect relationships between desired and achieved color fidelity. It would be desirable, therefore, to be able to define the gamut and select specific colors within the gamut based on external criteria. Correlation between color standards, such as Pantone colors, is one such example. Another example is the need to determine if a specific color measured, by a spectrophotometer, is within the gamut of the output device. However, it would be desirable to be able to reproduce a color or set of colors based on an altered gamut of the output device as affected by known preprocessing of image data.